Documents U.S. Pat. No. 5,919,080, U.S. Pat. No. 6,012,965 and US 2005/0173046 A1, describe a spectacle lens blocker designed for attaching a spectacle lens to a block piece without in that case contacting the spectacle lens, the block piece or a blocking ring. These blocking devices use a manual spectacle lens imaging and aligning station, in conjunction with two axes for automatic movement control for a spectacle lens receiving head in order to position the spectacle lens at a predetermined height and position above the block piece. In the simplest form of these devices the operator (after input of job data or downloading of the same from a host computer) thus begins to position a spectacle lens blank on the imaging station. The imaging station projects a plan view of the spectacle lens blank on a computer screen, while the computer at the same time inserts an image of the desired position and axial orientation of the spectacle lens blank on the same screen so as to superimpose these images.
The operator aligns the “true” image of the spectacle lens blank on the ideal image generated by the computer. The desired position is determined by the computer on the basis of the various job data which were calculated in correspondence with the prescription data desired by the end customer. The operator can move the spectacle lens blank forwardly or backwardly and position it in any desired angular position on the imaging station. When the operator has correctly aligned the spectacle lens blank, the operator confirms this by pressing a button.
The system computer then moves the spectacle lens receiving head with respect to the two aforesaid movement axes. The receiving head receives the spectacle lens in the position which the imaging station has predetermined and moves it to the blocking station. The block piece, which was inserted into the blocking station, is then held in the blocking station in a fixed and known position relative to the machine co-ordinate system. A blocking material can then flow in liquid state into the blocking station and the spectacle lens is placed by way of the aforesaid movement axis in the liquid blocking material. In that case, the spectacle lens contacts neither the block piece nor the casting mould, but is held only by the receiving head and can cure. The receiving head can then release the spectacle lens and the spectacle lens mounted, i.e. blocked on the block piece can be removed from the blocking station.
In the above-described prior art only four degrees of freedom can be taken into consideration in the blocker in order to position the spectacle lens on the block piece. Two of these degrees of freedom are determined by the operator by manual setting at the imaging station, while the other two degrees of freedom are provided by the two movement axes. However, six degrees of freedom (three translational and three rotational) are required in order to fully position an object in a desired three-dimensional co-ordinate system. Accordingly, absent from the outlined prior art are two degrees of freedom for fully positioning the spectacle lens with respect to the block piece, as can be expected in a conventional blocking method with a blocking ring for supporting the spectacle lens.
Compensation for these “errors” is provided in the above prior art in that these, if not known, are initially determined and then correction data are transmitted to the downstream processing machines. The movement control system of these downstream processing machines then has to have the degrees of freedom lacking in the blocker so that compensation can be provided for the above “errors” identified by the blocker. The processing machine thus has to “adapt” to the blocker or be “adapted” to this, which restricts the use of this blocker.
What is needed is a device for blocking workpieces, particularly spectacle lenses, for processing and/or coating thereof, which can be used as universally as possible without requiring specific processing machines or specific processing default settings in the downstream process.